Semiconductor device

ABSTRACT

According to one embodiment, a semiconductor device includes: a first region including: a first semiconductor layer; a first semiconductor region; a second semiconductor region; a third semiconductor region having higher impurity concentration than the first semiconductor region; a first electrode; a second electrode; an insulating film; a third electrode; a fourth electrode, a second region including a pad electrode, and the third region including: the first semiconductor layer; the first semiconductor region; a third semiconductor region; the first electrode; the second electrode; and a first insulating layer.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 14/015,145,filed Aug. 30, 2013, now allowed, which is based upon and claims thebenefit of priority from Japanese Patent Application No. 2013-107255,filed on May 21, 2013; the entire contents of each of which areincorporated herein by reference.

FIELD

Embodiments described herein relate generally to a semiconductor device.

BACKGROUND

Recently, demand for power MOSFETs has been growing, for instance, inapplications for driving vehicle-mounted motors such as in EPS(electrically-assisted power steering). The motor can be driven by e.g.a three-phase inverter and an H-bridge circuit. In a power MOSFET, arecovery current flows because of the presence of energization of theparasitic diode and reverse recovery operation. When this recoverycurrent flows, a prescribed breakdown voltage is required to avoiddestruction of the semiconductor by this current (in the following, thistolerance is referred to as trr withstand capability). This also appliesto the low-side MOSFET of a synchronous rectification DC-DC converter.

In this context, a trench gate MOSFET having a field plate structure hasbeen drawing attention. In such elements, higher trr withstandcapability is required.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a schematic plan view showing a semiconductor deviceaccording to a first embodiment, and FIG. 1B is a schematic plan viewshowing the region indicated by arrow A of FIG. 1A;

FIG. 2 is a schematic sectional view showing the semiconductor deviceaccording to the first embodiment;

FIG. 3A is a schematic plan view showing the function of thesemiconductor device according to the reference example, and FIG. 3B isa schematic sectional view at a position along line X-Y of FIG. 3A;

FIG. 4A is a schematic plan view showing the function of thesemiconductor device according to the first embodiment, and FIG. 4B is aschematic sectional view at a position along line X-Y of FIG. 4A;

FIG. 5A is a schematic plan view showing a semiconductor deviceaccording to a second embodiment, and FIG. 5B is a schematic sectionalview at a position along line X-Y of FIG. 5A;

FIG. 6 is a schematic plan view showing a semiconductor device accordingto a third embodiment;

FIG. 7A is a schematic plan view showing a semiconductor deviceaccording to a fourth embodiment, and FIG. 7B is a schematic sectionalview at a position along line X-Y of FIG. 7A;

FIG. 8 is a schematic plan view showing a semiconductor device accordingto a fifth embodiment; and

FIG. 9 is a schematic plan view showing a semiconductor device accordingto a sixth embodiment.

DETAILED DESCRIPTION

In general, according to one embodiment, a semiconductor deviceincludes: a first region; a second region; and a third region providedbetween the first region and the second region, the first regionincluding: a first semiconductor layer of a first conductivity type; afirst semiconductor region of a second conductivity type provided on thefirst semiconductor layer; a second semiconductor region of the firstconductivity type provided on the first semiconductor region; a thirdsemiconductor region of the second conductivity type being in contactwith the first semiconductor region, and the third semiconductor regionhaving higher impurity concentration than the first semiconductorregion; a first electrode electrically connected to the secondsemiconductor region and the third semiconductor region; a secondelectrode electrically connected to the first semiconductor layer; aninsulating film extending from a surface of the first semiconductorregion into the first semiconductor layer; a third electrode in contactwith the first semiconductor region via the insulating film; a fourthelectrode in contact with the first semiconductor layer and the thirdelectrode via the insulating film, the second region including a padelectrode electrically connected to the third electrode above the firstsemiconductor layer, and the third region including: the firstsemiconductor layer; the first semiconductor region provided on thefirst semiconductor layer; the third semiconductor region in contactwith the first semiconductor region; the first electrode electricallyconnected to the third semiconductor region; the second electrodeelectrically connected to the first semiconductor layer; and a firstinsulating layer extending from a position of the third semiconductorregion to a position of the first semiconductor layer.

Embodiments will now be described with reference to the drawings. In thefollowing description, like members are labeled with like referencenumerals, and the description of the members once described is omittedappropriately.

First Embodiment

FIG. 1A is a schematic plan view showing a semiconductor deviceaccording to a first embodiment. FIG. 1B is a schematic plan viewshowing the region indicated by arrow A of FIG. 1A.

The semiconductor device 1 according to the first embodiment is a powerMOSFET. The semiconductor device 1 includes an active region 1 a (firstregion), a gate pad region 1 g (second region), and an unused region(inactive region) 1 d (third region). For instance, the gate pad region1 g is juxtaposed with the active region 1 a. For instance, the unusedregion 1 d is juxtaposed with the active region 1 a and the gate padregion 1 g, and provided between the active region 1 a and the gate padregion 1 g. Part of the unused region 1 d is slightly projected to theside of the active region 1 a juxtaposed with the gate pad region 1 g.That is, the unused region 1 d is located near the corner of the gatepad region 1 g.

In the active region 1 a, active elements such as transistors or passiveelements such as built-in diodes (parasitic diodes) are placed. In thegate pad region 1 g, a pad electrode 38 is placed. The pad electrode 38is provided above the drift layer described later. The pad electrode 38is electrically connected to the gate electrode (gate electrode 30described later) of the MOSFET. In the unused region 1 d, no activeelement is placed.

In the semiconductor device 1, the active region 1 a is divided by theunused region 1 d. This is because of e.g. the following reason. Forinstance, electric field may locally concentrate on the corner of thepad electrode 38 indicated by arrow B. If the unused region 1 d is notprovided, the active region 1 a is placed also near the corner of thepad electrode 38. In this placement, the active region 1 a near thecorner of the pad electrode 38 is affected by the local electric fieldat the pad electrode corner. Then, the element may fail to operatenormally. To avoid this, in the semiconductor device 1, the unusedregion 1 d is placed near the corner of the pad electrode 38.

Furthermore, FIG. 1B illustrates a gate wiring 33 and a source wiring41. The gate wiring 33 is electrically connected to the pad electrode 38and the gate electrode. The source wiring 41 is electrically connectedto the source region described later.

FIG. 2 is a schematic sectional view showing the semiconductor deviceaccording to the first embodiment.

FIG. 2 shows a cross section at a position along line X-Y of FIG. 1B.

First, the structure of the active region 1 a is described.

In the active region 1 a, a plurality of MOSFETs are provided. TheMOSFET is a MOSFET having what is called a vertical electrode structure.

For instance, in the active region 1 a, on an n⁺-type drain layer 10, ann⁻-type drift layer 11 (first semiconductor layer) is provided. On thedrift layer 11, a p-type base region 20 (first semiconductor region) isprovided. On the base region 20, an n⁺-type source region 40 (secondsemiconductor region) is provided. Furthermore, a p⁺-type hole ejectionregion 25 (third semiconductor region) is juxtaposed with the sourceregion 40. The hole ejection region 25 is in contact with the baseregion 20. The concentration of the impurity element contained in thehole ejection region 25 is higher than the concentration of the impurityelement contained in the base region 20. The bottom of the hole ejectionregion 25 may be located above the junction between the drift layer 11and the base region 20, or may be located below this junction.

A source electrode (first electrode) 50 is electrically connected to thesource region 40 and the hole ejection region 25. A drain electrode 51(second electrode) is in contact with the drain layer 10. The driftlayer 11 is electrically connected to the drain electrode 51.

Furthermore, a gate electrode 30 (third electrode) extends from theposition of the source region 40 to the position of the drift layer 11.The gate electrode 30 reaches the drift layer 11. An insulating film 31is provided between the source region 40, the base region 20, and thedrift layer 11 on one hand and the gate electrode 30 on the other. Theinsulating film 31 provided between the source region 40, the baseregion 20, and the drift layer 11 on one hand and the gate electrode 30on the other may also be referred to as gate insulating film. The gateinsulating film extends e.g. from the surface of the base region 20 intothe drift layer 11. The gate electrode 30 is in contact with the driftlayer 11 via the gate insulating film.

The direction from the source electrode 50 toward the drain electrode 51is referred to as Z direction (first direction). A direction crossingthe Z direction is referred to as X direction (second direction). In theactive region 1 a, a field plate electrode 35 (fourth electrode) isjuxtaposed with the gate electrode 30 in the X direction. The fieldplate electrode 35 is electrically connected to the source electrode 50,or placed at a floating potential.

The field plate electrode 35 is in contact with the drift layer 11 viathe insulating film 31. The insulating film 31 is provided also betweenthe field plate electrode 35 and the gate electrode 30. The insulatingfilm 31 in contact with the field plate electrode 35 may also bereferred to as field plate insulating film. That is, the field plateelectrode 35 is in contact with the drift layer 11 and the gateelectrode 30 via the field plate insulating film. The thickness of theinsulating film 31 in contact with the field plate electrode 35 isthicker than the thickness of the insulating film 31 in contact with thegate electrode 30. An interlayer insulating film 27 is provided betweenthe source electrode 50 on one hand and the gate electrode 30 and thefield plate electrode 35 on the other. The structure of the unusedregion 1 d is now described.

In the unused region 1 d, on the drain layer 10, a drift layer 11 isprovided. On the drift layer 11, a base region 20 is provided. A holeejection region 25 is in contact with the base region 20. In the unusedregion 1 d, the bottom of the hole ejection region 25 may be locatedabove the junction between the drift layer 11 and the base region 20, ormay be located below this junction.

A source electrode 50 is electrically connected to the hole ejectionregion 25. A drain electrode 51 is in contact with the drain layer 10.The drift layer 11 is electrically connected to the drain electrode 51.

Furthermore, in the unused region 1 d, an insulating layer 32 (firstinsulating layer) is provided from the position of the hole ejectionregion 25 to the position of the drift layer 11. The depth of theinsulating layer 32 is equal to the depth of the insulating film 31. Inother words, the bottom of the insulating layer 32 is located at thesame position as the bottom of the insulating film 31. The pitch in theX direction of a plurality of insulating layers 32 may be equal to ordifferent from the pitch in the X direction of a plurality of insulatingfilms 31.

As an example, FIG. 2 shows a configuration in which the insulatinglayer 32 surrounds the lower end and the side portion of the field plateelectrode 35. Furthermore, on both sides of the field plate electrode35, a pair of gate electrodes 30 are provided.

The cross-sectional structure in the X-Z plane of the insulating layer32, the gate electrode 30, and the field plate electrode 35 in theunused region 1 d is the same as the cross-sectional structure in theX-Z plane of the insulating film 31, the gate electrode 30, and thefield plate electrode 35 in the active region 1 a. This is because theinsulating layer 32, the gate electrode 30, and the field plateelectrode 35 in the unused region 1 d is formed in the samemanufacturing process as the insulating film 31, the gate electrode 30,and the field plate electrode 35 in the active region 1 a. In the unusedregion 1 d, the field plate electrode 35 and the gate electrode 30 maybe removed appropriately.

An interlayer insulating film 27 is provided between the insulatinglayer 32 and the source electrode 50. The field plate electrode 35surrounded with the insulating layer 32 is electrically connected to thesource electrode 50, or placed at a floating potential. The gateelectrode 30 in the unused region 1 d is e.g. electrically connected tothe source electrode 50 or the pad electrode 38, or placed at a floatingpotential.

The base region 20, the source region 40, the hole ejection region 25,the field plate electrode 35, the insulating film 31, and the insulatinglayer 32 each extend in the Y direction. The length in the Y directionof each of the base region 20, the source region 40, the hole ejectionregion 25, and the field plate electrode 35 is different between in theactive region 1 a and in the unused region 1 d. The insulating layer 32may be shaped like a mesh or ring instead of a stripe extending in the Ydirection.

The material of the drain layer 10, the drift layer 11, the base region20, the source region 40, and the hole ejection region 25 is e.g.silicon (Si), silicon carbide (SiC), or gallium arsenide (GaAs). Thematerial of the source electrode 50, the drain electrode 51, and the padelectrode 38 can be e.g. at least one metal of aluminum (Al), nickel(Ni), copper (Cu), and titanium (Ti). The material of the gate electrode30 and the field plate electrode 35 includes e.g. polysilicon ortungsten (W). The material of the source wiring 41 and the gate wiring33 includes e.g. polysilicon or at least one metal of aluminum (Al),nickel (Ni), copper (Cu), and titanium (Ti). The insulating film and theinsulating layer according to the embodiment include e.g. silicondioxide (SiO_(x)) or silicon nitride (SiN_(x)).

The insulating film 31 and the insulating layer 32 are formed in atrench formed in the drift layer 11. Thus, the insulating film 31 andthe insulating layer 32 may be referred to as a trench structure.Furthermore, the gate electrode 30 may be referred to as trench gate.Thus, the MOSFET provided in the semiconductor device 1 may be referredto as a trench gate MOSFET having a field plate structure.

In FIG. 2, the MOSFET having a vertical electrode structure is shown.However, the embodiment also includes an IGBT (insulated gate bipolartransistor) in which a p⁺-type semiconductor layer is provided betweenthe drain electrode 51 and the drain layer 10. In the embodiment,n⁺-type, n-type, and n⁻-type may be referred to as first conductivitytype, and p⁺-type, p-type, and p⁻-type may be referred to as secondconductivity type. This notation means that the impurity concentrationis decreased in the order of n⁺-type, n-type, and n⁻-type, and in theorder of p⁺-type, p-type, and p⁻-type.

Here, the “impurity concentration” refers to the effective concentrationof the impurity element contributing to the conductivity of thesemiconductor material. For instance, in the case where thesemiconductor material contains an impurity element serving as a donorand an impurity element serving as an acceptor, the impurityconcentration is defined as the concentration of activated impurityelements except the donor and the acceptor canceling each other.

The n⁺-type, n-type, and n⁻-type impurity element can be e.g. phosphorus(P) or arsenic (As). The p⁺-type, p-type, and p⁻-type impurity elementcan be e.g. boron (B).

Before describing the function of the semiconductor device 1, thefunction of a semiconductor device according to a reference example isdescribed.

FIG. 3A is a schematic plan view showing the function of thesemiconductor device according to the reference example. FIG. 3B is aschematic sectional view at a position along line X-Y of FIG. 3A.

In the semiconductor device 100 according to the reference example, theaforementioned hole ejection region 25 is not provided in the unusedregion 1 d. Furthermore, in the unused region 1 d, although the trenchstructure exists on both sides thereof, the trench structure is notprovided elsewhere. In the semiconductor device 100, the unused region 1d is an omitted portion of the trench structure.

In such a structure, when the parasitic diode is turned on, holesinjected from the parasitic diode are easily accumulated in the unusedregion 1 d. The parasitic diode is e.g. a pn junction diode made of thehole ejection region 25 and the drift layer 11. For instance, in FIG.3B, holes accumulated in the drift layer 11 of the unused region 1 d areschematically denoted by the symbol “h”. Furthermore, in thesemiconductor device 100, the portion below the pad electrode 38 has thesame structure as the omitted portion of the trench structure. Thus,holes h are easily accumulated also below the pad electrode 38.Furthermore, holes h may be accumulated in the outer edge portion of thesemiconductor device 1 except the active region, except the unusedregion, and except the gate pad region.

Next, when the parasitic diode is turned off (at reverse recovery time,recovery time), for instance, the accumulated holes h reach the holeejection region 25 of the active region 1 a through the drift layer 11.For instance, as indicated by arrow P of FIG. 3A, the accumulated holesh flow into the hole ejection region 25 close to the unused region 1 d.Then, the holes h concentrate near the corner of the pad electrode 38where electric field concentrates. When the semiconductor is notsufficiently tolerant to this locally concentrating hole current, thesemiconductor device 100 is eventually destroyed. Thus, thesemiconductor device 100 may fail to achieve high trr withstandcapability.

In comparison, the function of the semiconductor device 1 is described.

FIG. 4A is a schematic plan view showing the function of thesemiconductor device according to the first embodiment. FIG. 4B is aschematic sectional view at a position along line X-Y of FIG. 4A.

In the semiconductor device 1 according to the first embodiment, aplurality of hole ejection regions 25 are provided in the unused region1 d. Furthermore, the unused region 1 d includes a trench structure. Theunused region 1 d is not an omitted portion as in the reference example.

At ON time of the MOSFET, holes injected from the parasitic diode may beaccumulated in the unused region 1 d. However, at OFF time (recoverytime) of the MOSFET, as indicated by arrow P of FIG. 4A, the accumulatedholes h flow out to the source electrode 50 through the hole ejectionregion 25 provided in the unused region 1 d. Furthermore, in thesemiconductor device 1, the trench structure is placed in the unusedregion 1 d. Thus, in the unused region 1 d of the semiconductor device1, the hole accumulation region is smaller than in the unused region 1 dof the semiconductor device 100.

Accordingly, in the semiconductor device 1, holes h do not easilyconcentrate near the corner of the pad electrode 38. Thus, in thesemiconductor device 1, local concentration of the hole current does noteasily occur. Accordingly, the aforementioned destruction does noteasily occur. Thus, in the semiconductor device 1, the hole currentinjected from the parasitic diode is efficiently extracted to the sourceelectrode 50 at recovery time. As a result, the semiconductor device 1has higher trr withstand capability.

Furthermore, the hole ejection region 25 and the trench structure can beformed in the unused region 1 d by changing the layout of the maskpattern. That is, in forming the hole ejection region 25 and the trenchstructure in the unused region 1 d, there is no need to increase themanufacturing step. Thus, no cost increase is incurred.

Second Embodiment

FIG. 5A is a schematic plan view showing a semiconductor deviceaccording to a second embodiment. FIG. 5B is a schematic sectional viewat a position along line X-Y of FIG. 5A.

The semiconductor device 2 according to the second embodiment furtherincludes an insulating layer 60 (second insulating layer) in addition tothe structure of the semiconductor device 1. The insulating layer 60extends from the source electrode 50 side to the drift layer 11 side.The insulating layer 60 extends from the source electrode 50 to thedrift layer 11. The insulating layer 60 may be referred to as dummytrench. The insulating layer 60 is provided outside the active region 1a and the unused region 1 d. In the semiconductor device 2, the activeregion 1 a and the unused region 1 d are surrounded with the insulatinglayer 60. The depth of the insulating layer 60 is equal to the depth ofthe insulating film 31 or the depth of the insulating layer 32.Alternatively, a similar effect is achieved even if these depths are notequal as long as being a desired depth not affecting thecharacteristics.

FIG. 5B shows a configuration in which the insulating layer 60 surroundsthe lower end and the side portion of the field plate electrode 35. Thefield plate electrode 35 surrounded with the insulating layer 60 iselectrically connected to the source electrode 50, or placed at afloating potential. This field plate electrode 35 may be removedappropriately.

Thus, in the semiconductor device 2, the injection of the hole currentfrom below the pad electrode 38 or the outer edge portion of thesemiconductor device 2 into the active region 1 a is further suppressedby the barrier of the insulating layer 60. As a result, thesemiconductor device 2 has higher trr withstand capability than thesemiconductor device 1.

Third Embodiment

The insulating layer 60 may surround the region other than the activeregion and the unused region.

FIG. 6 is a schematic plan view showing a semiconductor device accordingto a third embodiment.

The semiconductor device 3 according to the third embodiment furtherincludes an insulating layer 60 in addition to the structure of thesemiconductor device 1. The cross-sectional structure of the insulatinglayer 60 provided in the semiconductor device 3 is the same as thecross-sectional structure of the insulating layer 60 provided in thesemiconductor device 2. The insulating layer 60 provided in thesemiconductor device 3 is referred to as third insulating layer. Theinsulating layer 60 may surround the lower end and the side portion ofthe field plate electrode 35. In this case, the field plate electrode 35is electrically connected to the source electrode 50, or placed at afloating potential. This field plate electrode 35 may be removedappropriately. The insulating layer 60 extends from the source electrode50 side to the drift layer 11 side. The insulating layer 60 is providedoutside the gate pad region 1 g. In the semiconductor device 3, the gatepad region 1 g is surrounded with the insulating layer 60.

Thus, in the semiconductor device 3, the injection of the hole currentfrom below the pad electrode 38 into the active region 1 a is furthersuppressed by the barrier of the insulating layer 60. As a result, thesemiconductor device 3 has higher trr withstand capability than thesemiconductor device 1.

Fourth Embodiment

FIG. 7A is a schematic plan view showing a semiconductor deviceaccording to a fourth embodiment. FIG. 7B is a schematic sectional viewat a position along line X-Y of FIG. 7A.

The semiconductor device 4 according to the fourth embodiment furtherincludes an insulating layer 31 a in the gate pad region 1 g in additionto the structure of the semiconductor device 1. An interlayer insulatingfilm 70 is provided between the pad electrode 38 and the semiconductor.The insulating layer 31 a provided below the pad electrode 38 isreferred to as fourth insulating layer. In the semiconductor device 4,the drift layer 11 below the gate pad region 1 g is divided into aplurality by the insulating layers 31 a. That is, below the gate padregion 1 g, a plurality of insulating layers 31 a extend from thesurface of the drift layer 11 into the drift layer 11. In thesemiconductor device 4, the insulating film 31 placed in the activeregion 1 a extends to the gate pad region 1 g. This extended portion isreferred to as insulating layer 31 a. However, in the insulating layer31 a, the gate electrode 30 is not provided.

The insulating layer 31 a may surround the lower end and the sideportion of the field plate electrode 35. In this case, the field plateelectrode 35 is electrically connected to the source electrode 50, orplaced at a floating potential. This field plate electrode 35 may beremoved appropriately. Furthermore, the insulating film 31 placed in theactive region 1 a does not need to be extended to the gate pad region 1g, but there may be a discontinuity between the insulating film 31 andthe insulating layer 31 a. The pitch in the X direction of a pluralityof insulating layers 31 a may be equal to or different from the pitch inthe X direction of a plurality of insulating films 31.

In such a structure, the hole accumulation region of the drift layer 11of the gate pad region 1 g is reduced because of the presence of aplurality of insulating layer 31 a. The reduction of the holeaccumulation region of the drift layer 11 results in decreasing thedensity of holes h accumulated below the pad electrode 38. Thus, in thesemiconductor device 4, the injection of the hole current from below thepad electrode 38 into the active region 1 a is further suppressed. As aresult, the semiconductor device 4 has higher trr withstand capabilitythan the semiconductor device 1.

In FIG. 7B, the base region 20 is shown. However, below the padelectrode 38, the base region 20 may be removed. In this case, theportion of the base region 20 in FIG. 7B is occupied by the drift layer11. Also in this case, the same effect is achieved.

Fifth Embodiment

FIG. 8 is a schematic plan view showing a semiconductor device accordingto a fifth embodiment.

The semiconductor device 5 according to the fifth embodiment has acomposite structure of the semiconductor device 2 and the semiconductordevice 4. In such a structure, the injection of the hole current frombelow the pad electrode 38 or the outer edge portion of thesemiconductor device 5 into the active region 1 a is suppressed by thebarrier of the insulating layer 60. Furthermore, the density of holes haccumulated below the pad electrode 38 is decreased. Consequently, theinjection of the hole current from below the pad electrode 38 into theactive region 1 a is further suppressed. As a result, the semiconductordevice 5 has higher trr withstand capability than the semiconductordevices 1, 2, and 4.

Sixth Embodiment

FIG. 9 is a schematic plan view showing a semiconductor device accordingto a sixth embodiment.

In the semiconductor device 6 according to the sixth embodiment, in theactive region 1 a, the field plate electrode 35 is juxtaposed with thegate electrode 30 in the Z direction from the source electrode 50 towardthe drain electrode 51. That is, the field plate electrode 35 is locatedbelow the gate electrode 30. Such a structure also exhibits the samefunction as the semiconductor device 1.

The embodiments have been described above with reference to examples.However, the embodiments are not limited to these examples. Morespecifically, these examples can be appropriately modified in design bythose skilled in the art. Such modifications are also encompassed withinthe scope of the embodiments as long as they include the features of theembodiments. The components included in the above examples and thelayout, material, condition, shape, size and the like thereof are notlimited to those illustrated, but can be appropriately modified.

The term “on” in “a portion A is provided on a portion B” refers to thecase where the portion A is provided on the portion B such that theportion A is in contact with the portion B and the case where theportion A is provided above the portion B such that the portion A is notin contact with the portion B.

Furthermore, the components included in the above embodiments can becombined as long as technically feasible. Such combinations are alsoencompassed within the scope of the embodiments as long as they includethe features of the embodiments. In addition, those skilled in the artcould conceive various modifications and variations within the spirit ofthe embodiments. It is understood that such modifications and variationsare also encompassed within the scope of the embodiments.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the inventions. Indeed, the novel embodiments described hereinmay be embodied in a variety of other forms; furthermore, variousomissions, substitutions and changes in the form of the embodimentsdescribed herein may be made without departing from the spirit of theinventions. The accompanying claims and their equivalents are intendedto cover such forms or modifications as would fall within the scope andspirit of the invention.

What is claimed is:
 1. A semiconductor device comprising: a firstregion; and a second region being adjacent to the first region, thefirst region including: a first semiconductor layer of a firstconductivity type; a first semiconductor region of a second conductivitytype provided on the first semiconductor layer; a second semiconductorregion of the first conductivity type provided on the firstsemiconductor region; a first electrode electrically connected to thesecond semiconductor region; a second electrode electrically connectedto the first semiconductor layer; a third electrode facing the firstsemiconductor layer, the first semiconductor region, and the secondsemiconductor region via an insulating film; and a fourth electrodefacing the first semiconductor layer and the third electrode via theinsulating film, the second region including: the first semiconductorlayer of a first conductivity type; the first semiconductor region of asecond conductivity type provided on the first semiconductor layer; thefourth electrode facing the first semiconductor layer and the firstsemiconductor region via the insulating film; and a pad electrodeprovided on the first semiconductor layer, and electrically connected tothe third electrode.
 2. The device according to claim 1, furthercomprising: a first insulating layer extending from the first electrodeto the first semiconductor layer, wherein the first region is surroundedwith the first insulating layer.
 3. The device according to claim 2,wherein depth of the first insulating layer is equal to depth of theinsulating film.
 4. The device according to claim 1, wherein the fourthelectrode is electrically connected to the first electrode, or apotential of the fourth electrode is a floating potential.
 5. The deviceaccording to claim 1, further comprising: a second insulating layerextending from the first electrode side to the first semiconductor layerside, wherein the second region is surrounded with the second insulatinglayer.
 6. The device according to claim 1, wherein the fourth electrodeis juxtaposed with the third electrode in a second direction crossing afirst direction from the first electrode toward the second electrode.